This invention relates to electrical connections to flexible circuitry tapes and the like. More particularly, the invention relates to a method of making soldered electrical connections to a flexible circuit tape where solder connection areas or pads are on an inaccessible side of the tape.
Flexible circuits generally comprise a strip or tape of flexible plastic or other electrically insulating material, for example a polyester sold under the name Mylar or a polyimide sold under the name Kapton both of which are trademarks of E. I. DuPont deNemours & Co., Wilmington, Del. Electrical circuit patterns are formed on or in such insulating material. Usually, such flexible circuit tapes have electrical contact areas or pads on one surface of the tape, which makes electrical contact with respective individual circuit patterns embedded in the tape so as to permit connecting these circuit patterns to other external or remotely located circuit elements or electrical devices. These contact areas are generally in the form of small pads of solderable material. One such flexible circuit tape is in the form of a keyhole comprising a generally circular portion having a rectangularly shaped portion integral therewith. The circuit patterns permit connection, as by the aforementioned solder pads, to a plurality of circularly arranged electromagnetic coils, for example, which may be positioned atop of the circular portion. The circuit patterns terminate in the rectangular portion in contact with additional solder pads in the rectangular portion to permit connection of the electromagnetic coils to other circuit elements. The contact areas or solder pads are all disposed on the same surface of the flexible circuit tape, it being extremely difficult or otherwise impractical to provide some solder pads on one side of the tape, and other solder pads on the opposite side thereof. In seeking to provide external connections to the flexible circuit tape by means of a multi-pin terminal or connector block, which usually is in the form of a rigid printed circuit board, the terminal block rests upon the solder pads disposed on the rectangular portion and thus makes the solder pads thereon inaccessible for soldering.
U.S. Pat. No. 4,342,883 to Wernet et al. deals with the making of electrical connections to a flexible circuit tape. While teaching the soldering of pins inserted through the flexible circuit, the solderable contact areas of the flexible circuit tape in this patent are all disposed on a surface of the tape which is accessible to soldering. In other words, the pins are inserted through the flexible circuit from the opposite side of the circuit tape to that on which the contact areas are provided. Hence, for example, the multi-pin connector block in this patent does not mask or render inaccessible the contact areas from soldering. Nor do these patentees teach how the pins are inserted through the flexible tape.
In most instances, it is customary in such flexible circuit applications to pre-drill holes through the tape and/or contact areas and insert the pins therethrough to the contact areas on the opposite sides thereof, where they may be soldered to the contact areas. However, where there are a plurality of such contact areas closely spaced from each other in a relatively small area, such pre-drilling is difficult and expensive. The difficulty in such an instance will be appreciated when one contemplates the necessity of inserting 20 pins through a flexible circuit tape in an area that is about 5 mm. wide by 25 mm. in length, with the corresponding number of contact areas, each being about 0.060 inches in diameter and spaced apart about 0.125 inches center-to-center.
In U.S. Pat. No. 4,343,530 to L. J. Leger, a mail terminal is disclosed having a V-shaped stem which is inserted in a pre-drilled circular hole in a printed circuit board. The V-shape of the stem is provided to increase the strength and the solder wicking action through the hole in the printed circuit board. Leger's pre-drilled hole is plated through with copper prior to insertion therethrough of the terminal stem, after which the terminal stem is secured to the board by soldering the stem and the base of the terminal, thereby being secured in and to the copper-plated hole of the printed circuit board. Again, it will be noted, pre-drilling is required, pre-plating of the hole is necessary and a specially shaped terminal stem must be utilized.